GtkEntryCompletion::set_minimum_key_length

void set_minimum_key_length(int length);

Sets the minimum length of the search key to the value specified by
length. This means that the key string
(contents of the GtkEntry) must be at least
length characters before a completion list
will be displayed. This is useful for long lists, where completing
using a small key will take too much time and will likely return a
too large dataset.